Questions tagged [ip]

For questions about Internet Protocol (IP), an OSI layer-3 network protocol. There are two current IP versions in use: IPv4 and IPv6.

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93
votes
6answers
584k views

How do you calculate the prefix, network, subnet, and host numbers?

Example: IP: 128.42.5.4 In binary: 10000000 00101010 00000101 00000100 Subnet: 255.255.248.0 How could you determine the prefix, network, subnet, and host numbers?
7
votes
2answers
806 views

NAT Overlapping

I am trying to do some networking lab. Basically, I have a network like this: So, is it possible to configure NAT router in such way, that PC1 and PC2 can access remote HOST and each other. The ...
58
votes
7answers
16k views

Why are IPv4 addresses running out?

I understand that we are running out (or ran out already?) of IPv4 addresses, but I don't really understand why that is. Right now, every home has its own IPv4 address (dynamically assigned, but still,...
18
votes
7answers
6k views

Does CIDR really “do away” with IP address classes?

I am still struggling to understand to what extent CIDR really renders IP address classes obsolete. Here's what I understood so far: It's ridiculously inefficient (and impossible, too) to assign ...
3
votes
4answers
1k views

Can IP packet with TTL=1 reach loopback interface of a switch?

This is a question that bothers me a lot. And I cannot argue with colleagues because all switches I see can response the ping request even my TTL=1. So my question is, does TTL decrease between ...
6
votes
1answer
871 views

Why can I ping IP addresses from 127.0.0.1 to 127.255.255.254?

I thought that the loopback IP address of my machine is 127.0.0.1. I do not understand why am I able to ping IP addresses until 127.255.255.254.
5
votes
2answers
2k views

Why do LANs use MAC addressing instead of IP addressing?

Why do LANs use MAC addressing instead of IP addressing? In other words, why can't a network just assign an IP address to a local area network device and send the data to that, instead of the MAC ...
3
votes
1answer
1k views

minimum hop limit for a packet where there are n routers between source and destination

I am having some confusion while calculating he minimum hop limit ... consider following scenario: (source)-------(R1)--------(R2)--------(destination) Now when an IP datagram is supposed to travel ...
1
vote
2answers
181 views

Does the same IP cause IP conflict if one is from /22 other is from /24?

I have two hosts. They both have the same IP/subnet, ex.: 1.2.3.4/24 on both. I know this is bad, since there will be duplicate IP in the network. OK. But: If I have different (?) ranges: 1.2.3.4/...
3
votes
2answers
2k views

Broadcasting traffic by 255.255.255.255 or by “subnet dot all ones”?

If a device wants to broadcast traffic does it send it to the "all ones" IP? (Which is 255.255.255.255)? Or does it send it to "the all ones of the subnet"? (For example if the subnet is 123.123.0.0/...
3
votes
1answer
947 views

Can a 172.168.10.0/28 be a class B Subnet

I am starting my studies in networking and starting off with the basics of IP addressing and Subnetting with CIDR values. My Question here is 1st how can you tell the subnet class of an IP address ...
3
votes
1answer
566 views

What is the point of a subnet mask on a local network?

I have a question regarding subnet masks and my understanding (or misunderstanding of them). So when a subnet mask is used, a bitwise AND is performed using the subnet mask and the IP address(es). ...
3
votes
3answers
196 views

Is it possible to perform a Layer 2 (MAC address) traceroute?

I understand the difference between layer2 & layer3 and MAC & IP. I understand address resolution protocol, etc. But is there any way to do a traceroute that will show Layer 2 information? For ...
-1
votes
2answers
9k views

Calculating Fragmentation offset doubt

Suppose we have a data of 4500 bytes which passes through 2 routers of MTU 2600 and 1400 respectively. What will be the resulting fragments at the 2nd router (1400 MTU one)? The 4 fragments at 2nd ...
39
votes
4answers
21k views

How to check for a valid public IP address?

Consider a list of IP addresses as provided by the X-Forwarded-For HTTP header: 10.0.0.142 , 192.168.0.10 , 212.43.234.12 , 54.23.66.43 I would like to know which is the first publicly-accessible ...
8
votes
3answers
9k views

Is a TCP three-way handshake required for an HTTP POST?

I don't quite understand if i posting http form data from the browser to the server, does the protocol still need to make three-way handshake (syn-ack-data) or it only works for GET http requests?
23
votes
1answer
114k views

TCPDump - Filter by MAC Address

I would like to display all traffic for or from a specific MAC address. For that I tried sudo tcpdump host aa:bb:cc:11:22:33 It does not work and returns me an error tcpdump: pktap_filter_packet: ...
19
votes
1answer
3k views

What is the practical use of a /31 CIDR or 255.255.255.254?

With a /31 subnet, we are left with zero usable hosts. The /31 subnet only has two hosts - one for network and another for broadcast. I am wondering why would someone ever use this subnet.
13
votes
4answers
1k views

Possible (bit) patterns of a netmask

Given a prefix Y, it's easy to calculate the corresponding netmask: Put Y times a set bit, and then fill up "to the right" with zeros until one has 32 bits (IPv4) in total. Example: Prefix 24, thus ...
14
votes
2answers
3k views

Why are there 3 ranges of private IPv4 addresses?

Why are there three separate ranges of private IPv4 addresses of different sizes? Why not just reserve the largest (10.0.0.0 - 10.255.255.255) range and let people create /16 or /24 (or whatever) ...
6
votes
4answers
3k views

Why do I get “% Warning: use /31 mask on non point-to-point interface cautiously” when I use a /31 subnet mask?

Why do I get % Warning: use /31 mask on non point-to-point interface cautiously when I use a /31 subnet mask over Ethernet, and why am I not able to ping from R1 to R2 when both the interfaces have ...
5
votes
1answer
660 views

Who assigns IP s to the ISP s?

How a particular ISP get it's IP ? Is there any centralized authority to distribute IP s ?
3
votes
1answer
386 views

Finding Subnet Ranges of IPv6

I need to find a single subnet range to cover 10,000 IP addresses (hosts), given the IPv6 Address 2405:1300:c5c1:322::/108 (for example) I am aware of how to do subnet in IPv4 but cannot grasp the ...
2
votes
2answers
2k views

Is there any difference between Limited Broadcasting and Directed Broadcasting when used in same network

I understand that limited broadcasting happens locally and can be done by using destination address as 255.255.255.255. The directed broadcasting happens across networks. To be precise, i want to ...
6
votes
2answers
2k views

Why maximum length of IP, TCP, UDP packet is not suit?

From many tutorials, I get follow knowledge(maybe I'm misunderstood) : maximum of an Ethernet packet is about 1500 bytes. maximum of an IP packet is about 65535 bytes. maximum of a UDP packet is ...
5
votes
3answers
1k views

IP Address vs MAC Address, how does that really work together illustration

My question is simple, i don't really know if I understand it so I'm asking. Why do we have both addresses, if we know the ip address of the target and source computer, why do we need some physical ...
4
votes
4answers
613 views

Is there a valid scenario where a router is used to translate a public IP address?

NAT typically refers to router translating an IP address from a private network to a public IP address so that the node on the private network can access public Internet. Is there a valid scenario ...
4
votes
1answer
646 views

IPv6 Link-local addresses

RFC 4291 specifies that IPv6 link-local unicast addresses must have a high-order bit sequence of 1111111010, or fe80::/10. However, the same document specifies that the 54 bits following the first 10 ...
3
votes
3answers
3k views

IPv6 NAT with Link-Local Address

It's more than usual to find NAT translating IPv4 private addresses (such as 192.168.0.0/16 or 10.0.0.0/8) to non private addresses. Is it possible that NAT translates even IPv6 link-local addresses (...
3
votes
1answer
72 views

Is 802.1x port security enforces IP uniqueness

I know that 802.1x can track MAC addresses. If MAC address is used on one port then you can prohibit it from being used on another port. Can 802.11x protocol do the same thing for IP addresses? My ...
3
votes
2answers
632 views

What is the point of ARP?

I'm a complete beginner at networking, but if I've understood this correctly, the gist of ARP is: We want to use high level adresses to the highest degree possible but ultimately, we actually need ...
3
votes
5answers
17k views

Identifying an IP address conflict through a Cisco Switch

I have a 3550 Catalyst Switch. 2 computers connected to the switch have the same IP address configured and there is an IP address conflict. How do i zero in on these computers with just the CLI of ...
2
votes
1answer
86 views

IP address that can not be reached from outside of device

I am sorry if this is a silly question, but I am developing an application that should connect to itself over sockets, but to make it secure it should only be reachable from local device. I believe I ...
2
votes
2answers
744 views

Which layers of the protocol stack does a border router access for which purpose?

Dataflows on the internet are often depicted as going from one host via at least two border routers to another host. In these illustrations, the hosts are equipped with and make use of the full ...
2
votes
3answers
898 views

Same IP addresses with different CIDR notations, is it possible?

Can we have exactly same IP addresses with different CIDR notations? Example: 194.24.0.20/20 194.24.0.20/21 194.24.0.20/16 194.24.0.20/24 194.24.0.20/29 194.24.0.20/15 And so on... How will it ...
1
vote
1answer
358 views

Why does OSPF use flooding instead of broadcasting?

In flooding, we send unicast/multicast frames to all the routers in the network, whereas in broadcasting, we have a broadcast address by which we send packets to all the routers. In OSPF, "Router ...
1
vote
2answers
213 views

Link Local Address using in NDP (IPv6)

How is using of link local address in NDP. We can discover neighbor by using global address. So why we need link local address in NDP?
1
vote
1answer
84 views

Unsecured devices and IPv6

I'm currently starting to read up on IPv6, and as soon as I heared that every device can/will have a public accessible adreess i got a little freaked out. There are a lot of horror stories about ...
1
vote
1answer
36 views

Remote Host Neighbor Cache Entry State after Neighbor Solicitation request

When a Host A sends for the first time a NS request to another Host B, host B answers with a NA. In Host A Neighbor Cache, the state Entry for host B gets from INCOMPLETE to REACHABLE, when NA comes ...
1
vote
1answer
84 views

What's the relationship of a Router with its loopback interface in logic?

I have a Router1 with a loopback 0 connected to the Router2: the interface brief is bellow: Router1>show ip interface brief Interface IP-Address OK? Method Status ...
-1
votes
3answers
635 views

How do 2 PCs learn each other's IP addresses for ARP resolution? [closed]

So, if one PC will use another PC's IP address for ARP resolution, how does the PC sending the ARP Request even know which IP address to call for in the first place? What happens in a scenario where ...